1. Field of the Invention
The present invention relates to a device for operation of a sliding door member.
2. Description of the Prior Art
The invention has been developed primarily for application to Suburban Train Doors and will be described with reference to this particular application. However, it will be appreciated that the invention is not limited to this particular field of use.
The train doors to which this invention applies are of the type comprising two planar door members disposed in the closed position in edge to edge abutment, which are slid apart in the same plane during opening. Each door member requires an individual operating device usually utilizing a push stroke to open, and a pull stroke to close.
The requirements of a suitable operating device include the ability to lock the doors in the closed position whilst the train is in motion. Most importantly a "soft nose" closing stroke is also required, whereby the closing force is reduced over the last part of the stroke to prevent crushing people or objects that may be trapped between the closing doors. In most applications it is also advantageous that any locking device can be manually overridden to unlock the doors if the train air supply falls below a minimum safe running pressure.
The "soft nose" stroking has hitherto been achieved by use of mechanical and air cushion springs, requiring a hollow piston rod to house such devices. However, such designs preclude the use of conventional latching methods.
It is an object of the present invention to provide a device for operation of a sliding door member which will overcome or substantially ameliorate at least some of the disadvantages of the prior art.